Natural Resources Conservation Service Ecological site R040XA115AZ Sandy Wash 10"-13" p.z. Accessed: 09/25/2021 General information Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site. Figure 1. Mapped extent Areas shown in blue indicate the maximum mapped extent of this ecological site. Other ecological sites likely occur within the highlighted areas. It is also possible for this ecological site to occur outside of highlighted areas if detailed soil survey has not been completed or recently updated. MLRA notes Major Land Resource Area (MLRA): 040X–Sonoran Basin and Range AZ 40.1 – Upper Sonoran Desert Elevations range from 2000 to 3200 feet and precipitation averages 10 to 13 inches per year. Vegetation includes saguaro, palo verde, mesquite, creosotebush, triangle bursage, prickly pear, cholla, limberbush, wolfberry, bush muhly, threeawns, ocotillo, and globe mallow. The soil temperature regime is thermic and the soil moisture regime is typic aridic. This unit occurs within the Basin and Range Physiographic Province and is characterized by numerous mountain ranges that rise abruptly from broad, plain-like valleys and basins. Igneous and metamorphic rock classes dominate the mountain ranges and sediments filling the basins represent combinations of fluvial, lacustrine, colluvial and alluvial deposits. Associated sites R040XA114AZ Loamy Upland 10"-13" p.z. R040XA116AZ Sandy Upland 10"-13" p.z. R040XA117AZ Sandy Loam Upland, Deep 10"-13" p.z. R040XA118AZ Sandy Loam Upland 10"-13" p.z. Similar sites R041XB213AZ Sandy Wash 8-12" p.z. R041XC316AZ Sandy Wash 12-16" p.z. R040XB216AZ Sandy Wash 7"-10" p.z. Table 1. Dominant plant species Tree (1) Parkinsonia florida (2) Prosopis velutina Shrub (1) Ambrosia ambrosioides Herbaceous (1) Muhlenbergia porteri (2) Sphaeralcea ambigua Physiographic features This site occurs in the upper elevations of the Sonoran Desert in southern Arizona. This site benefits on a regular basis from extra moisture received as over bank flooding and/or runoff from adjacent upland sites. It occurs on flood plains and low stream terraces. Table 2. Representative physiographic features Landforms (1) Alluvial fan (2) Flood plain (3) Stream terrace Flooding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Flooding frequency Rare to occasional Ponding duration Very brief (4 to 48 hours) to brief (2 to 7 days) Ponding frequency None to rare Elevation 1,900–3,300 ft Slope 0–3% Aspect Aspect is not a significant factor Climatic features Precipitation in the sub resource area ranges from 10 to 13 inches in the southern part, along the Mexican border with elevations from about 1900 to 3200 feet. Precipitation in the northern part of the resource area ranges from 11 to 14 inches with elevations from about 1700 to 3500 feet. Winter-summer rainfall ratios range from 40%-60% in the southern portions of the land resource unit, to 50%-50% in the central portions, to 60%-40% in the northern part of the land resource unit. As one moves from east to west in this resource area rains become slightly more unpredictable and variable with Coefficients of Variation of annual rainfall equal to 29% at Tucson and 36% at Carefree. Summer rains fall July through Sept., originate in the Gulf of Mexico, and are convective, usually brief, intense thunderstorms. Cool season moisture tends to be frontal, originating in the Pacific and Gulf of California. This winter precipitation falls in widespread storms with long duration and low intensity. Snow is rare and seldom lasts more than an hour or two. May and June are the driest months of the year. Humidity is generally very low. Winter temperatures are mild, with very few days recording freezing temperatures in the morning. Summer temperatures are warm to hot, with several days in June and July exceeding 105 degrees F. Both the spring and the summer growing seasons are equally important for perennial grass, forb and shrub growth. Cool and warm season annual forbs and grasses can be common in their respective seasons with above average rainfall. Perennial forage species can remain green throughout the year with available moisture. Table 3. Representative climatic features Frost-free period (average) 265 days Freeze-free period (average) 0 days Precipitation total (average) 13 in Influencing water features There are no water features associated with this site. Soil features These are very young soils on gravelly and sandy alluvium of mixed origin. They are deep and excessively well drained. Textures range from sandy loam to very gravelly sands. Although course textures make for low water holding capacities, plant-soil moisture relationships are good due to the extra moisture the soils receive. They may or may not be calcareous. Soils mapped on this site include: in SSA-627 Southern Mohave County MU Anthony-7; SSA-645 Aguilla-Carefree MU's Arizo-6, 7 & 8, Anthony-121; SSA-661 Eastern Pinal Southern Gila counties MU Queencreek-295; SSA-666 MU Queencreek-200; SSA-668 Tucson Avra Valley MU's Anthony-AhA, AnA, AnB, ApB, AsB & Vu, Arizo- Az, Brazito-Br, BsB & Bt, Comoro-Cm & Co, Gravelly Alluvial Land-Gr & VgB, Vinton-VsA & Vu; SSA-669 Eastern Pima county MU's Anthony-3 & Arizo-5. Table 4. Representative soil features Surface texture (1) Very gravelly sandy loam (2) Fine sandy loam (3) Very gravelly loamy sand Family particle size (1) Sandy Drainage class Somewhat excessively drained to well drained Permeability class Rapid to moderately rapid Soil depth 60 in Surface fragment cover <=3" 5–40% Surface fragment cover >3" 0–5% Available water capacity 3–6 in (0-40in) Calcium carbonate equivalent 0–5% (0-40in) Electrical conductivity 0–2 mmhos/cm (0-40in) Sodium adsorption ratio 0–2 (0-40in) Soil reaction (1:1 water) 7.4–8.4 (0-40in) Subsurface fragment volume <=3" 0–65% (Depth not specified) Subsurface fragment volume >3" 0–10% (Depth not specified) Ecological dynamics The plant communities found on an ecological site are naturally variable. Composition and production will vary with yearly conditions, location, aspect, and the natural variability of the soils. The Historical Climax Plant Community represents the natural potential plant communities found on relict or relatively undisturbed sites. Other plant communities described here represent plant communities that are known to occur when the site is disturbed by factors such as fire, grazing, or drought. Production data provided in this site description is standardized to air dry weight at the end of the summer growing season. The plant communities described in this site description are based on near normal rainfall years. NRCS uses a Similarity Index to compare existing plant communities to the plant communities described here. Similarity Index is determined by comparing the production and composition of a plant community to the production and composition of a plant community described in this site description. To determine Similarity Index, compare the production (air dry weight) of each species to that shown in the plant community description. For each species, count no more than the maximum amount shown for the species, and for each group, count no more than the maximum amount shown for the group. Divide the resulting total by the total normal year production shown in the plant community description. If the rainfall has been significantly above or below normal, use the total production shown for above or below normal years. If field data is not collected at the end of the summer growing season, then the field data must be corrected to the end of the year production before comparing it to the site description. The growth curve can be used as a guide for estimating production at the end of the summer growing season. State and transition model Figure 4. State and Transition, Sandy Wash 10-13" pz. State 1 Historical Climax Plant Community Community 1.1 Historical Climax Plant Community The potential plant community is a diverse mixture of desert trees, shrubs, vines, grasses, and forbs. Major species are well dispersed throughout the plant community. The aspect is shrubland. With continuous, heavy grazing, perennial mid grasses and palatable forbs are removed from the plant community. When the grass cover has been depleted, erosion begins and sandy channels form which remove flood water rapidly and tend to dry the site. With erosion, trees like mesquite, blue paloverde, and retama increase to dominate the site. As palatable understory species are removed, increases occur in shrubs like big bursage, burrowbush, creosotebush, and wolfberry. Base level changes in watersheds can lead to eventual gullying of this site. Under deteriorated conditions, channel areas develop and are pioneered by shrubs like burrobush and big bursage. Table 5. Annual production by plant type Low Representative Value High Plant Type (Lb/Acre) (Lb/Acre) (Lb/Acre) Grass/Grasslike 175 600 1000 Forb 30 450 800 Tree 250 500 700 Shrub/Vine 62 250 410 Total 517 1800 2910 Table 6. Soil surface cover Tree basal cover 1-2% Shrub/vine/liana basal cover 1-2% Grass/grasslike basal cover 3-8% Forb basal cover 1-2% Non-vascular plants 0% Biological crusts 0-10% Litter 40-80% Surface fragments >0.25" and <=3" 5-65% Surface fragments >3" 0-15% Bedrock 0-5% Water 0% Bare ground 10-50% Table 7. Canopy structure (% cover) Grass/ Height Above Ground (Ft) Tree Shrub/Vine Grasslike Forb <0.5 – – 1-5% 0-5% >0.5 <= 1 – 0-1% 5-15% 1-10% >1 <= 2 – 0-2% 10-25% 1-15% >2 <= 4.5 – 1-5% 0-5% 0-5% >4.5 <= 13 1-10% 1-5% – – >13 <= 40 10-15% – – – >40 <= 80 – – – – >80 <= 120 – – – – >120 – – – – Figure 6.